Simon 1997: what it reports on intrapatient escalation
Reading notes, with every number sourced to a page
Notes on Simon R, Freidlin B, Rubinstein L, Arbuck SG, Collins J, Christian MC. Accelerated titration designs for phase I clinical trials in oncology. J Natl Cancer Inst 1997;89(15):1138–1147. doi:10.1093/jnci/89.15.1138
Read for the design definitions and the simulation results. The model-fitting sections and the worked trial example were not read. Every number below carries the journal page it came from.
Simon numbers his cohort designs 1 to 4 and letters his intrapatient options A and B. Neither matches this project’s designs A (conventional), A2 (accelerated), B (catch-up) and C (scout-and-backfill).
Separating the Two Effects
Against design 1, the paper’s designs 2, 3 and 4 change two things at once: they accelerate the cohort structure, and they turn on intrapatient dose escalation. The two effects can still be separated, because the paper also reports the mixed designs: design 1 with intrapatient escalation, and designs 2 to 4 without it (p.1143–1144).
Intrapatient escalation reduces the number of patients treated at subtherapeutic doses, and changes nothing else the paper measures. Everything that shortens the trial comes from the cohort structure, and specifically from the dose step size.
The Two Escalation Options
| Option | Grade 0–1 last course | Grade 2 | Grade 3 or worse |
|---|---|---|---|
| A | stay | stay | de-escalate one level |
| B | escalate | stay | de-escalate one level |
Option A is conventional practice, with no within-patient escalation. Option B is the mechanism this project’s catch-up design uses. The grade 2 column is inferred: the Appendix states only the escalate and de-escalate conditions.
Double Steps, With and Without Intrapatient Escalation (3A vs 3B)
Design 3 is one patient per dose level with double dose steps during the accelerated stage, reverting to design 1 at the first first-course dose-limiting toxicity (DLT) or the second first-course grade 2 event. 3A and 3B differ only in whether an individual patient’s dose escalates.
| Metric | 3A, no IPDE | 3B, with IPDE | Difference | Source |
|---|---|---|---|---|
| Patients, mean | not reported | 20.7 | stated as “little or no effect” | 3B p.1141; claim p.1143 |
| Patients, median | not reported | 19.3 | — | p.1141 |
| Cohorts, the paper’s time proxy | not reported | Fig. 3 only | stated as “little or no effect” | Fig. 3 p.1143; claim p.1143 |
| Patients whose worst toxicity was grade 0–1 | 6.5 | 3.9 | B treats 2.6 fewer at subtherapeutic doses | 3A p.1144; 3B p.1142 |
| Patients with grade 3 | 5.7 | 6.8 | B has 1.1 more | 3A p.1143; 3B p.1142 |
| Patients with grade 4 | 3.2 | 4.3 | B has 1.1 more | 3A p.1143; 3B p.1142 |
The toxicity-grade counts are the only quantities the paper gives as numbers for both A and B. Patients and cohorts are a qualitative claim.
Standard Cohorts, With and Without Intrapatient Escalation (1A vs 1B)
The cleaner comparison, because no acceleration is involved. Design 1 is cohorts of three expanding to six, with single dose steps throughout, so 1A against 1B is intrapatient escalation alone.
| Metric | 1A, no IPDE | 1B, with IPDE | Source |
|---|---|---|---|
| Patients | 39.9 mean, 36.7 median | “no effect … compared with 1A” | 1A p.1141; claim p.1143 |
| Cohorts | baseline | “no effect … compared with 1A” | p.1143 |
| Patients whose worst toxicity was grade 0–1 | 23.3 | 19.3 | p.1143 |
On a conventional cohort structure, intrapatient escalation moves 4 patients out of the undertreated group and changes neither the sample size nor the duration.
Where the Time Saving Comes From
All four rows are the paper’s default pairings: design 1 with option A, designs 2 to 4 with option B (p.1143).
| Design | Early stage | Step size | Patients, mean | Patients, median | Cohorts against design 1 |
|---|---|---|---|---|---|
| 1 | 3–6 per level throughout | single (~40%) | 39.9 | 36.7 | baseline |
| 2 | 1 per level | single (~40%) | 24.4 | 21.8 | no advantage; design 1 slightly fewer |
| 3 | 1 per level | double (~100%) | 20.7 | 19.3 | substantial saving |
| 4 | 1 per level | double (~100%) | 21.2 | 19.1 | substantial saving |
Fewer patients does not mean a shorter trial. Design 2 enrols 15 fewer patients than design 1 and saves no time. Design 1 needs slightly fewer cohorts than design 2, “because design 2 sometimes overshoots its target and requires more cohorts at de-escalated levels” (p.1142). The saving appears only with double dose steps: designs 3 and 4 “show substantial savings over designs 1 and 2 because of their use of double dose steps during the initial stage of the trials” (p.1142). The paper tabulates cohorts separately from patients to make this point (p.1142).
What the Paper Does Not Report
- No figure or table splits option A from option B. Figures 1 to 4 each carry four panels, one per design, in the default pairings only. The whole A-against-B comparison is four sentences of running text on p.1143–1144.
- No numeric value for cohorts. Fig. 3 (p.1143) is twenty-bin histograms of the average cohort count across the 20 parameter sets, for the four default designs. A number read off it by eye would still not be an A-against-B number.
- No calendar time in weeks or months. Cohorts are the proxy, defined as “time to completion when there is an excess of patients available for entry in the trial” (Fig. 3 caption, p.1143).
- No separate 3A sample size. The claim covering it is “combining designs 2 through 4 with option A also has little or no effect on the number of patients or cohorts required compared with the same design using option B” (p.1143).
Consequences for the Specification
Catch-up helps patients, not the clock: supported in direction, unquantified in size. The paper reports that catch-up escalation helps participants more than it shortens the trial, and the participant half has a number attached: 3.9 against 6.5 patients at subtherapeutic doses (p.1142, p.1144). The trial-duration half is a qualitative claim in both comparisons. Cite Simon for the direction. The simulation still has to produce the time saving, because there is no published number to use instead.
The conventional comparator is 3A: one patient per dose level, double dose steps, no intrapatient escalation, reverting to design 1 at the first first-course DLT or the second first-course grade 2. It captures the acceleration without the mechanism under study, and Objection 3 in Section 27 requires it to be simulated. It is Design A2 in the specification.
Time is bought with step size, not with who escalates. This is the finding that carries over. The dose escalation factor in Section 13 becomes the mechanism rather than a parameter, and the scout ladder’s step sizes are what the design has to defend.
The null result applies to catch-up and not to the scout. Simon’s intrapatient escalation moves patients up into levels the single-patient cohorts have already opened, which is why it adds no time. The catch-up design in Section 6 does exactly that and inherits the null result. The scout climbs into levels no cohort has opened, on a weekly interval rather than at a cohort review.
Other Literature on the Time Effect
A literature search found no paper that quantifies the calendar-time effect of intrapatient dose escalation. What follows comes from search results and abstracts, none of it read.
Guo et al. 2025 is the one paper that could still report it (IP-CRM, Pharmaceutical Statistics, doi:10.1002/pst.2461). It is the only design paper that puts intrapatient escalation inside a comparative simulation. Its stated motivation is patient scarcity, in paediatric and rare-cancer trials where accrual limits the design, rather than calendar time, so its tables probably resolve sample size rather than duration.
The literature that does quantify trial duration works by a different mechanism. The time-to-event family, starting with TITE-CRM (Cheung and Chappell, Biometrics 2000;56:1177–1182), reports trial duration directly in its simulations. It shortens trials by letting the next patient enrol before the current one has completed the DLT observation window, without changing any individual patient’s dose.
That split fits the null result above. Within-patient escalation moves patients through dose levels that have already been cleared, so it cannot make the highest cleared level rise faster, and the field treats trial duration as a problem of accrual and observation windows instead.
The time-to-event mechanism is independent of the scout, and is a separate lever on \(\Delta T\). It is listed under future work in Section 27b of the specification and is not in v1.